Historically, there have been a number of ways to fill or obturate a root canal space. After a tooth has been thoroughly shaped and debrided of diseased nerve tissue, a filling of the space is required to prevent the ingress of contaminants from both the top section of the root canal (coronal) and the bottom portion (apical). The goal is a hermetic seal of the root canal system. The most common cause of failure of root canals is bacterial contamination either through microleakage or contamination during the process. The better the seal can be accomplished, the greater the long term prognosis of the tooth.
Initially silver points were used to fill the canal space, but due to leakage problems associated with their shape and the material itself, this technique was abandoned. This was replaced with the cold lateral filling by forcible condensation of gutta percha points.
Gutta percha is a naturally occurring trans isomer of rubber itself that can be modified into points. Gutta percha is typically formulated into a tapered conical shape (such as a 0.02 taper) to assume the tapered conical shape of the apical end of the root canal of a tooth. Because it is malleable, gutta percha at times has been inserted as an obturator. An obturator is a pointed instrument having a tapered distal end core and a cylindrical handle at the other end. The malleable gutta percha is wrapped around the tapered distal end core of the obturator instrument, and the handle is grasped manually. However, grasping the obturator manually often obstructs the view of the delivery process of the obturator into the root canal site.
Using a separate tapered carrier core for introducing gutta percha wrapped around it often results in uneven dislodging or stripping of the heated gutta percha from the obturator instrument.
Therefore, there is a need for an integral one piece gutta percha core/cone of the present invention, which acts as its own carrier, which can strongly bond to a thin layer of cement coating the inner walls of a root canal. This gutta percha core/cone of the present invention is used at ambient room temperature, (not heated), and therefore is not subject to stripping or shrinkage.
Depending upon the commercial brand, gutta percha cones contain 18–23% pure gutta percha. Waxes, resins, fillers, zinc oxide, and barium sulfate comprise the remainder of the filling material (cones) known by the colloquial trade name of “gutta percha”.
The cold lateral condensation filling technique employs a series of sequentially intertwined gutta percha cones placed in a sea of cement. The cement formula originally was a zinc oxide eugenol cement. Although popular, this technique was subject to voids as a result of the lateral condensation filling and inaccuracies of adaptation to the root canal wall. It is very difficult with lateral condensation filling to achieve a three dimensional seal of the root canal system.
The next change in the condensation filling process was the introduction of thermoplastic techniques that heated the gutta percha with hand instruments before insertion of the gutta percha into the apical end of the root canal. The rationale behind thermoplastic gutta percha is that heated gutta percha flows and will more readily adapt to irregularities in the root canal system. Unfortunately, heated gutta percha flows only a few millimeters and shrinks upon cooling, thereby not filling the root canal space it was intended to fill and seal. Consequently, the use of a luting agent is recommended with all thermoplastic techniques. While seemingly attractive, heated gutta percha has its limitations. Shrinkage upon cooling and being technique sensitive are two of the limitations.
A further development in the obturation process was the introduction of alpha phase gutta percha inside the root canal on a carrier (plastic or metal). The combination of gutta percha on a carrier was referred to as an obturator. The success of this technique had the limitation of being dictated by the success of the preparation. If the taper of the preparation was not sufficient, the tooth structure could strip (denude) the gutta percha from the carrier, thereby reducing the success of the technique. A carrier that has a portion stripped of gutta percha increases the risk of bacterial contamination and therefore reduces the prognosis.
Recently, Endodontics has been witness to numerous heated gutta percha techniques that all have the common problem of shrinkage. Additionally, some of these techniques are technically sensitive making the use of thermoplastic techniques particularly challenging for the general practitioner.
There also was the concept of filling the entire root canal with a cement or paste, not utilizing gutta percha. This method had numerous problems such as lack of control of the material, and serious shrinkage that resulted in leakage and bacteria contamination. Revisement challenges were also a factor if the root canal procedure had to be re-treated.
Additionally, more recently, the concept of a single cone of gutta percha used with a large amount of cement has been advocated by Ultradent Incorporation with their ENDO-EZE® technique and its related Anatomic Endodontic Technology (AET)™ technique, using their ENDO-REZ® resin sealer.
However, the lack of synchronicity between the root canal preparation and the cone is a problem, as well as the cements, which do not adapt and bond well to the walls of the preparation or to the gutta percha itself. With the use of the Ultra Dent ENDO-EZE® preparation and the AET™ technique with the ENDO-REZ® resin sealer, there is inconsistency between the root canal preparation and the gutta percha used to fill the root canal space. Therefore, the lack of a precise match between the preparation and the gutta percha itself results in either excess cement (that will shrink) or the gutta percha cone can hang up in the coronal part of the canal and therefore, not reach the end of the root canal preparation intended to be sealed by the gutta percha. This can result in leakage and bacterial contamination thereby reducing the prognosis of the case.
However, Koch et al. and others, showed in 1993 that glass ionomer cement in its original formulation offered promise as a single cone cement to hold the gutta percha seal in place within the root canal. Other authors still expressed concern with the bond of the glass ionomer cement to the gutta percha. In other words, while the bond of the glass ionomer to dentin was superior to other sealers, the bond to gutta percha was merely adequate. Another concern is the real probability that the large amount of cement in a single cone technique, as a thick layer of cement, will shrink more than a thin layer of cement. This potential problem is the result of a lack of synchronicity between the root canal preparation and the gutta percha cone. As an example, one cannot place a 0.02 taper gutta percha cone into a 0.04 taper preparation and expect good results. The cone must match the tapered and/or curved shape preparation of the root canal in as precise a manner as possible.
Furthermore, the restoration of endodontically treated teeth has been subject to a lack of synchronicity between the root canal preparation and a prefabricated post. The consequence of this disparity is less than ideal retention of the post, as well as a weakening of the root when posts of greater dimension, or different shapes, are utilized, thereby compromising the long-term success of the restoration and the tooth.
An additional concern of the restoration of endodontically treated teeth is the lack of a proper coronal seal. The lack of a three dimensional seal (on top of the gutta percha in the root canal) can result in an ingress of bacterial components. Bacterial contamination will result in failure of the root canal and remains a serious concern in modern endodontics.